Ac/dc power converter

ABSTRACT

In one embodiment, an AC/DC power converter can include: a rectifier bridge and a filter capacitor for converting an external AC voltage to a half-sinusoid DC input voltage; a first storage component, where during each switching cycle in a first operation mode, a first path receives the half-sinusoid DC input voltage to store energy in the first storage component, and a first current through the first storage component increases; a second storage component, where a second path receives a second DC voltage to store energy in the second storage component, and a second current through the second storage component increases; and a third storage component, where in a second operation mode, the first current decreases to release energy from the first to the third storage component, where the second DC voltage includes a voltage across the third storage component through a third path.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No.201210428797.6, filed on Oct. 31, 2012, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention generally pertains to an electronic technology,and more particularly to an AC/DC power converter.

BACKGROUND

AC/DC power converters used to convert an AC voltage to a constant DCelectric signal (DC voltage and/or DC current) are widely applied todrive loads of relatively high power (e.g., electric motors,light-emitting diode [LED] lamps, etc.). A rectifying bridge is usuallyconfigured in an AC/DC power converter to convert an external AC voltageto a half-sinusoid DC voltage for a subsequent converting circuit. Also,a power factor correction (PFC) circuit may be utilized in an AC/DCpower converter to achieve power factor correction to obtain arelatively high power factor.

SUMMARY

In one embodiment, an AC/DC power converter can include: (i) a rectifierbridge and a filter capacitor configured to convert an external ACvoltage to a half-sinusoid DC input voltage; (ii) a first storagecomponent, where during each switching cycle in a first operation mode,a first path is configured to receive the half-sinusoid DC input voltageto store energy in the first storage component, and a first currentflowing through the first storage component is configured to increase;(iii) a second storage component, where a second path is configured toreceive a second DC voltage to store energy in the second storagecomponent, and a second current flowing through the second storagecomponent is configured to increase, where the first and second pathsshare a power switch; (iv) a third storage component, where in a secondoperation mode, the first current is configured to decrease to releaseenergy from the first storage component to the third storage component,where the second DC voltage includes a voltage across the third storagecomponent through a third path; (v) where the energy stored in thesecond storage component is configured to be released to a load througha fourth path; and (vi) where a duration of the first operation mode ismaintained such that a peak value of the first current is in directproportion to the half-sinusoid DC input voltage, and an outputelectrical signal of the AC/DC power converter is maintained as pseudoconstant.

Embodiments of the present invention can advantageously provide severaladvantages over conventional approaches. For example, particularembodiments can provide a simplified AC/DC power converter structure toachieve a higher power factor and a substantially constant outputelectrical signal. Other advantages of the present invention may becomereadily apparent from the detailed description of preferred embodimentsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an example single stage AC/DC powerconverter.

FIG. 2 shows a schematic diagram of an example two stage AC/DC powerconverter.

FIG. 3A shows a schematic diagram of a first example AC/DC powerconverter in accordance with embodiments of the present invention.

FIG. 3B shows an example conductive path of the AC/DC power converter ofFIG. 3A during a first operation mode.

FIG. 3C shows an example conductive path of the AC/DC power converter ofFIG. 3A during a second operation mode.

FIG. 4A shows a schematic diagram of a second example AC/DC powerconverter in accordance with embodiments of the present invention.

FIG. 4B shows an example conductive path of the AC/DC power converter ofFIG. 4A during a first operation mode.

FIG. 4C shows an example conductive path of the AC/DC power converter ofFIG. 4A during a second operation mode.

FIG. 4D shows example operation waveforms of the AC/DC power converterof FIG. 4A.

FIG. 5A shows a schematic diagram of a third example AC/DC powerconverter in accordance with embodiments of the present invention.

FIG. 5B shows an example conductive path of the AC/DC power converter ofFIG. 5A during a first operation mode.

FIG. 5C shows an example conductive path of the AC/DC power converter ofFIG. 5A during a second operation mode.

FIG. 6A shows a schematic diagram of a fourth example AC/DC powerconverter in accordance with embodiments of the present invention.

FIG. 6B shows an example conductive path of the AC/DC power converter ofFIG. 6A during a first operation mode.

FIG. 6C shows an example conductive path of the AC/DC power converter ofFIG. 6A during a second operation mode.

FIG. 7A shows a schematic diagram of a fifth example AC/DC powerconverter in accordance with embodiments of the present invention.

FIG. 7B shows example waveforms of current through an inductor andcurrent through a primary winding.

FIG. 7C shows example conduction paths of the AC/DC power converter ofFIG. 7A when the power switch and a diode are turned on.

FIG. 7D shows example conduction paths of the AC/DC power converter ofFIG. 7A when the power switch and another diode are on.

FIG. 7E shows an example conduction path of the AC/DC power converter ofFIG. 7A when the power switch is turned off.

FIG. 8A shows a schematic diagram of a sixth example AC/DC powerconverter in accordance with embodiments of the present invention.

FIG. 8B shows an example conductive path in a first operation mode ofthe AC/DC power converter of FIG. 8A.

FIG. 8C shows an example conductive path in a second operation mode ofthe AC/DC power converter of FIG. 8A.

FIG. 9A shows a schematic diagram of a seventh example AC/DC powerconverter in accordance with embodiments of the present invention.

FIG. 9B shows an example conductive path in a first operation mode ofthe AC/DC power converter of FIG. 9A.

FIG. 9C shows an example conductive path in a second operation mode ofthe AC/DC power converter of FIG. 9A.

DETAILED DESCRIPTION

Reference may now be made in detail to particular embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention may be described in conjunction with thepreferred embodiments, it may be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set fourth in order to provide a thoroughunderstanding of the present invention. However, it may be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, processes, components, structures, and circuitshave not been described in detail so as not to unnecessarily obscureaspects of the present invention.

Either single stage converter or two stages converter can be usedachieve power factor correction (PFC), and a substantially constantoutput electric signal. With reference to FIG. 1, an example singlestage AC/DC power converter is shown. The single stage AC/DC powerconverter can include single stage PFC main circuit 10 implemented as aflyback topology. Also, single stage PFC controlling circuit 20 caninclude closed loop current controlling circuit 21, current controllingcircuit 22, zero-crossing trigger circuit 23, isolation circuit, andmultiplier U5.

The output current of single stage PFC main circuit 10 may be sampled byclosed loop current controlling circuit 21, the output of which can beisolated by an isolation circuit. The input voltage Vdc and the outputof the isolation circuit can be multiplied through multiplier U5, theoutput of which can be coupled to a non-inverting input terminal ofcurrent controlling circuit 22. The inverting terminal of the currentcontrolling circuit 22 can receive the input current. The output ofcurrent controlling circuit 22 can be coupled to zero-crossing triggercircuit 23, which can include voltage comparator U3 and RS flip-flop U4.The output of current controlling circuit 22 can be coupled to the resetterminal R, and the output of voltage comparator U3 can be coupled tothe set terminal S of RS flip-flop U4.

The on and off operation of switch S maybe controlled by the outputsignal of RS flip-flop U4 such that the input current is in phase withthe input voltage, to improve the power factor of the single stage PFCcircuit. However, “ripple” waves may exist in the output currentutilising the example implementation of FIG. 1. Further, the larger theripple wave is, the larger the error of the output current is. The inputcurrent may not follow the input voltage due to a larger error of theinput current, which can decrease the power factor.

Referring now to FIG. 2, a schematic diagram of an example AC/DC powerconverter with two stages (201 and 202) is shown. In this example, theAC/DC power converter can include power stages 203-1 and 203-2, andcontrol circuits 204-1 and 204-2. Power stage 203-1 can be controlled bycontrol circuit 204-1 such that the input current follows ahalf-sinusoid DC input voltage coupled to power stage 203-1 to achievepower factor correction. Power stage 203-2 can receive output voltageV_(out1) of stage 201. Also, power stage 203-2 can be controlled bycontrol circuit 203-2 to maintain a substantially constant outputcurrent to drive light-emitting diode (LED) load 207.

Improved harmonic wave performance and a higher power factor can beachieved by the example AC/DC power converter of FIG. 2. The DC voltageinput to a DC/DC stage can be pre-regulated by the independent PFC stageto make the output voltage more accurate, and the loading capacitor mayprovide an improvement that can be applied to higher power application.However, there are at least two control circuits, and at least two powerswitches, possibly resulting in more components, higher costs, lowerpower efficiency, and higher power losses. Thus, the particular exampleAC/DC power converter of FIG. 2 may not be suitable for some low andmedium power applications.

In one embodiment, an AC/DC power converter can include: (i) a rectifierbridge and a filter capacitor configured to convert an external ACvoltage to a half-sinusoid DC input voltage; (ii) a first storagecomponent, where during each switching cycle in a first operation mode,a first path is configured to receive the half-sinusoid DC input voltageto store energy in the first storage component, and a first currentflowing through the first storage component is configured to increase;(iii) a second storage component, where a second path is configured toreceive a second DC voltage to store energy in the second storagecomponent, and a second current flowing through the second storagecomponent is configured to increase, where the first and second pathsshare a power switch; (iv) a third storage component, where in a secondoperation mode, the first current is configured to decrease to releaseenergy from the first storage component to the third storage component,where the second DC voltage includes a voltage across the third storagecomponent through a third path; (v) where the energy stored in thesecond storage component is configured to be released to a load througha fourth path; and (vi) where a duration of the first operation mode ismaintained such that a peak value of the first current is in directproportion to the half-sinusoid DC input voltage, and an outputelectrical signal of the AC/DC power converter is maintained as pseudoconstant.

Referring now to FIG. 3A, shown is a schematic diagram of a firstexample AC/DC power converter in accordance with embodiments of thepresent invention. External AC voltage V_(AC) can be rectified andfiltered by a rectifier bridge and capacitor C₁ to generatehalf-sinusoid DC input voltage V_(in) across capacitor C₁. AC/DC powerconverter 300 can include inductor L₂ (first energy storage component),inductor L₃ (second energy storage component) and capacitor C₆ (thirdenergy storage component). The periods of energy storage and energydissipation of inductor L₂, inductor L₃, and capacitor C₆ may becontrolled through different paths to achieve higher power factor and asubstantially constant output electrical signal by virtue of thecharacteristics of the various energy storage components.

With reference to FIG. 3B, an example conductive path of the AC/DC powerconverter in a first operation mode is shown, where power switch Q₂ isturned on. In a first path (denoted by an encircled 1) can includeinductor L₂, power switch Q₂, and capacitor C₁. As inductor currenti_(L2) of inductor L₂ continues to increase, energy can be stored ininductor L₂. Simultaneously, in a second path (denoted by an encircled2), which can include inductor L₃, power switch Q₂ and capacitor C₆, theinductor current of inductor L₃ can continue to increase, and energy maybe stored in inductor L₃.

With reference to FIG. 3C, an example conductive path of the AC/DC powerconverter in a second operation mode is shown, where power switch Q₂ isturned off. In a third path (denoted by an encircled 3), which caninclude inductor L₂, diode D₆, and capacitor C₆, inductor current i_(L2)flowing through inductor L₂ can continue to decrease to release energy,which may be transferred to capacitor C₆ by charging. If the capacitanceof capacitor C₆ is sufficiently large, the voltage across capacitor C₆can maintain a substantially constant value with little fluctuation.Simultaneously, the inductor current of inductor L₃ can continue todecrease, and the energy of which may be released to the load throughthe fourth path (denoted by an encircled 4), which can include inductorL₃, diode D₆, and capacitor C₅.

Here, a boost power stage is configured by the first and third paths toreceive half-sinusoid DC input voltage V_(in), and to generatesubstantially constant voltage V_(bus) across capacitor C₆ with largercapacitance. Also, a buck power stage may be configured by the secondand fourth paths to receive voltage V_(bus) across capacitor C₆, and togenerate a substantially constant output current I_(o) to drive the load(e.g., LED lamps). As for the AC/DC power converter of FIG. 3A, thefirst path of the boost power stage and the second path of the buckpower stage can share power switch Q₂. Further, the third path of theboost power stage and the fourth path of the buck power stage can shareoutput diode D₆.

A protection circuit can also be included in the AC/DC power converterof FIG. 3A to prevent the current of the second path from beingtransferred to the input terminal. The protection circuit can includediode D₅ coupled between inductor L₂ and power switch Q₂ of the firstpath. Diode D₇ coupled between diode D₅ and inductor L₃ of the secondpath can also be included to prevent the inductor current of inductor L₃from being negative.

A current sensing circuit can be configured in the second path to detectthe current of the second path (e.g., the inductor current of inductorL₃), to derive output current information. Specifically, samplingresistor R_(sen) can be included in the current sensing circuit. Theoutput current can be derived from the voltage across sampling resistorR_(sen) representative of a peak inductor current. A controlling anddriving signal can be generated in accordance with the output current bycontrolling and driving circuit 303 to control operation of power switchQ₂, to achieve power factor correction and a substantially constantoutput current.

The circuit implementation and various example conductive paths indifferent (e.g., first and second) operation modes of the AC/DC powerconverter of FIG. 3A have been described above. Example operation ofpower factor correction and a substantially constant output electricalsignal of the AC/DC power converter of FIG. 3A will also be describedherein.

Based on operating principles of buck power stages, when the inductorcurrent is operated in a boundary conduction mode (BCM), the outputcurrent can be calculated as per formula (1) below.

$\begin{matrix}{I_{o} = {{\frac{V_{bus} - V_{o}}{2L_{m\; 3}} \times D \times T_{s}} = {\frac{V_{bus} - V_{o}}{2L_{m\; 3}} \times t_{on}}}} & (1)\end{matrix}$

Here, I_(o) is representative of the output current of the buck powerstage, L_(m3) is representative of the inductance of inductor L₃, D isrepresentative of the duty cycle of the buck power stage, V_(bus) isrepresentative of the voltage across capacitor C₆, which is input to thebuck power stage as the input voltage, V_(o) is representative of theoutput voltage of the buck power stage, t_(on) is representative of theon time of power switch Q₂, and T_(s) is representative of the switchingcycle of power switch Q₂.

If the on time t_(on) of power switch Q₂ can be controlled to besubstantially constant, output current I_(o) can be substantiallyconstant due to the substantially constant value of inductance L_(m3) ofinductor L₃, input voltage V_(bus), and output voltage V_(o). The peakinput current I_(inpk) can be calculated as per the following formula(2) in accordance boost power stage operating principles.

$\begin{matrix}{I_{inpk} = {\frac{V_{in}}{L_{m\; 2}} \times t_{on}}} & (2)\end{matrix}$

Here, I_(inpk) is representative of the peak input current, V_(in) isrepresentative of the half-sinusoid dc input voltage, L_(m2) isrepresentative of the inductance of inductor L₂, and t_(on) isrepresentative of the on time of power switch Q₂. Since the inductanceL_(m2) of inductor L₂ and on time t_(on) are substantially constant,peak input current I_(inpk) may be directly proportional tohalf-sinusoid dc input voltage V_(in) to achieve a higher power factor.

One skilled in the art will recognize that the on time of power switchQ₂ can be controlled to be substantially constant by employing availableconstant on-time controlling and driving circuits in accordance withoutput current feedback information I_(FB). In this example, when powerswitch Q₂ is turned on, the first and second paths can share powerswitch Q₂. Also, when power switch Q₂ is turned off, the third andfourth paths can share diode D₆. A boost power stage can include thefirst and third paths configured to achieve the power factor correction.Also, a buck power stage can include the second and fourth paths toachieve a substantially constant output electrical signal, and thesecond and fourth paths can share controlling and driving circuit 303.In this way, an improved power factor and steadier output current withfewer ripple waves can be applicable in relatively power applications(e.g., an LED driver).

Referring now to FIG. 4A, shown is a schematic diagram of a secondexample AC/DC power converter in accordance with embodiments of thepresent invention. AC/DC power converter 400 can include inductor L₁ asthe first energy storage component, transformer T₁ including primarywinding W_(p) and secondary winding W_(s) as the second energy storagecomponent, and capacitor C₂ as the third energy storage component. Also,a first path (denoted by an encircled 1), a second path (denoted by anencircled 2), a third path (denoted by an encircled 3), and a fourthpath (denoted by an encircled 4) are also included, and we will bediscussed with reference to FIGS. 4B and 4C.

Referring now to FIG. 4B, shown is an example conductive path in a firstoperation mode of the AC/DC power converter of FIG. 4A. In the firstoperation mode, power switch Q₁ is turned on. Inductor current i_(L1) ofinductor L₁ can continue to increase to store energy in the first path,which can include inductor L₁, power switch Q₁, and capacitor C₁.Simultaneously, inductor current i_(wp) of primary winding W_(p) cancontinue to increase to store energy in transformer T₁ in the secondpath, which can include primary winding W_(p), power switch Q₁, andcapacitor C₂.

Referring now to FIG. 4C, shown is an example conductive path in asecond operation mode of the AC/DC power converter of FIG. 4A. In thesecond operation mode, power switch Q₁ is turned off. In the third path,which can include inductor L₁, diode D₂, and capacitor C₂, inductorcurrent i_(L1) can continue to decrease to release energy to capacitorC₂ by charging. When the capacitance of capacitor C₂ is sufficientlyhigh, voltage V_(bus) across capacitor C₂ can be maintained assubstantially constant with minimal fluctuation. Simultaneously,inductor current i_(ws) of second winding W_(s) can continue to decreaseto release the energy of transformer T₁ to the load through the fourthpath, which can include secondary winding W_(s), diode D₃, and capacitorC₃.

Here, the first and third paths can form a boost power stage to receivehalf-sinusoid DC input voltage V_(in), and to generate a substantiallyconstant voltage V_(bus) across capacitor C₂. The second and fourthpaths can form a flyback power stage to receive voltage V_(bus), and togenerate a substantially constant output current I_(o) to drive the load(e.g., LED lamps). The boost power stage and the flyback power stage canshare power switch Q₁ and controlling and driving circuit 403.

A protection circuit can also be included in the AC/DC power converterof FIG. 4A to keep the current of the second path from reflowing to theinput terminal, and to keep the primary winding of the transformer fromshort-circuiting. For example, diode D₁ coupled between inductor L₁ andpower switch Q₁ of the first path can be included in the protectioncircuit. The circuit structure and the conductive paths of differentoperation modes of the AC/DC power converter of FIG. 4A have beendescribed herein. Also, controlling principles of power factorcorrection and constant output electric signal of the AC/DC powerconverter of FIG. 4A will be described below.

The output current I_(o) of the AC/DC power converter can be calculatedas per formula (3) in accordance with operation principles of theflyback power stage.

$\begin{matrix}{I_{o} = {I_{pk} \times \frac{n}{2} \times \frac{t_{off}}{t_{s}}}} & (3)\end{matrix}$

Here, I_(o) is representative of output current of flyback power stage,I_(pk) is representative of peak current of primary winding oftransformer T₁, n is representative of the turn ratio of secondarywinding W_(s) and primary winding W_(p) of transformer T₁, t_(off) isrepresentative of the off time of power switch Q₁, and i_(s) isrepresentative of the switching period of power switch Q₁. For example,off time t_(off) of power switch Q₁ can be calculated as below informula (4).

$\begin{matrix}{t_{off} = {t_{on} \times \frac{V_{bus}}{n \times V_{o}}}} & (4)\end{matrix}$

Here, t_(on) is representative of on time of power switch Q₁, V_(o) isrepresentative of output voltage of the AC/DC power converter, V_(bus)is representative of the voltage across capacitor C₂ that can beconfigured as the input voltage of the flyback power stage. Peak currentI_(pk) of primary winding W_(p) of formula (3) can be calculated as informula (5) below.

$\begin{matrix}{I_{pk} = {\frac{V_{bus}}{L_{p}} \times t_{on}}} & (5)\end{matrix}$

Here, L_(p) is representative of the inductance of primary winding W_(p)of transformer T₁. Formulas (4) and formula (5) may be substituted intoformula (3), to derive formula (6) below.

$\begin{matrix}{I_{o} = {\frac{V_{bus}}{L_{p}} \times t_{on} \times \frac{n}{2} \times \frac{V_{bus}}{{n \times V_{o}} + V_{bus}}}} & (6)\end{matrix}$

Since voltage V_(bus) and output voltage V_(o) can be maintained assubstantially constant, and inductance L_(p) of inductor L₁ and turnratio n are constant values, if on time t_(on) of power switch Q₁ can becontrolled to be substantially constant, a substantially constant outputcurrent I_(o) can be achieved. Input current I_(in) of the AC/DC powerconverter can be calculated as formula (7), in accordance with theoperation principles of boost power stages.

$\begin{matrix}{I_{inpk} = {\frac{V_{in}}{L_{m\; 1}} \times t_{on}}} & (7)\end{matrix}$

Here, I_(inpk) is representative of peak input current, V_(in) isrepresentative of half-sinusoid DC input voltage V_(in), and L_(m1) isrepresentative of inductance of inductor L₁. Since inductance L_(m1) ofinductor L₁ is constant, if on time t_(on) is substantially constant,peak input current I_(inpk) may be in direct proportion withhalf-sinusoid DC input voltage V_(in) to achieve a higher power factor.Thus for the AC/DC power converter of FIG. 4A, both constant outputcurrent and power factor correction can be achieved if the on time ofpower switch Q₁ can be controlled to be substantially constant.

Referring now to FIG. 4D, example operation waveforms of the AC/DC powerconverter of FIG. 4A are shown. In the example that inductor current isoperating in boundary conduction mode (BCM), the peak envelope of inputcurrent I_(in) may be indicated as a half-sinusoid waveform to achieve amuch higher power factor. The current waveforms of current throughprimary winding W_(p) and secondary winding of transformer T₁ areindicated as waveform i_(wp) and waveform i_(ws), respectively. Peakcurrent of primary winding W_(p) can be maintained as constant, and ontime of power switch Q_(i) can be maintained as constant that is therising time of current through primary winding W_(p).

Controlling and driving circuit 403 may be configured to generatedriving signal V_(G) in accordance with output current informationI_(FB) of AC/DC power converter to control operation of power switch Q₁to maintain on time that is substantially constant. In this way, ahigher power factor and substantially constant output current can beachieved.

The output current information can be obtained through various ways,such as an auxiliary winding coupled to primary winding, or samplingoutput current directly and being transferred to controlling and drivingcircuit 403 at the primary side of the transformer by an opticalcoupler, or employing any primary side controlling mode. Controlling anddriving circuit 403 can be configured to control operation of powerswitch Q₁ based on the output current information, which can utilize anysuitable circuit structures.

Furthermore, a current sampling circuit can also be included in thesecond path. Inductor current flowing through primary winding W_(p),independent of inductor current of the first path, can be sampled by thecurrent sampling circuit because the current sampling circuit isconfigured in the second path that can store energy in transformer T₁through primary winding W_(p). Controlling and driving circuit 403 cancontrol the on time of power switch Q₁ to be substantially constant toachieve power factor correction and a substantially constant outputelectrical signal in accordance with the sampled current information ofthe current sampling circuit.

For example, the current sampling circuit can include sampling resistorR_(sen) coupled between power switch Q₁ and ground. Also, one terminalof capacitor C₂ can be coupled to primary winding W_(p), while the otherterminal may be coupled to ground. The voltage across sampling resistorR_(sen) can be representative of the inductor current of primary windingW_(p) when power switch Q₁ is on, and output current information I_(FB)can be derived therefrom.

Referring now to FIG. 5A, shown is a schematic diagram of a thirdexample AC/DC power converter in accordance with embodiments of thepresent invention. Here, AC/DC power converter 500 can include inductorW_(p2) as the first energy storage component, inductor L₅ as the secondenergy storage component, and capacitor C₈ as the third energy storagecomponent.

Referring now to FIG. 5B, shown is an example conductive path of theAC/DC power converter of FIG. 5A in a first operation mode. In the firstoperation mode, power switch Q₃ can be turned on, and the inductorcurrent of inductor W_(p2) can continue to increase to store energy ininductor W_(p2) through a first path (denoted by an encircled 1), whichcan include inductor W_(p2), power switch Q₃, and capacitor C₁.Simultaneously, the inductor current flowing through inductor L₅ cancontinue to increase to store energy in inductor L₅ through a secondpath (denoted by an encircled 2), which can include inductor L₅, powerswitch Q₃, and capacitor C₈.

Referring now to FIG. 5C, shown is an example conductive path of theAC/DC power converter of FIG. 5A in a second operation mode. In thesecond operation mode, power switch Q₃ is turned off, and the inductorcurrent of inductor W_(s2) can continue to decrease to release energy tocapacitor C₈ by charging through third path (denoted by an encircled 3),which can include inductor W_(s2), diode D₈, and capacitor C₈. When thecapacitance of capacitor C₈ is sufficiently large, voltage V_(bus)across capacitor C₈ can be maintained as substantially constant withminimal fluctuation. Simultaneously, the inductor current of inductor L₅can continue to decrease, and the energy of inductor L₅ may release tothe load through a fourth path (denoted by an encircled 4), which caninclude inductor L₅, diode D₁₀, and capacitor C₉.

Here, the first and third paths may form an isolated flyback power stageto receive half-sinusoid DC input voltage V_(in), and to generate aconstant voltage V_(bus) across capacitor C₈ with a sufficiently largecapacitance. The second and fourth paths can form a buck power stage toreceive voltage V_(bus) across capacitor C₈, and to generate asubstantially constant output voltage V_(o) and a substantially constantoutput current I_(o) to drive the load (e.g., LED lamps). The first andsecond paths of the AC/DC power converter of FIG. 5A can share powerswitch Q₃ and controlling and driving circuit 503.

A protection circuit can also be included in the AC/DC power converterof FIG. 5A. For example, the protection circuit can include diode D₁₁coupled between primary winding W_(p2) and secondary winding W_(s2), anddiode D₈ coupled between capacitor C₁ and primary winding W_(p2). DiodeD₈ can be configured to keep the current from reflowing to the inputterminal when the input voltage is lower. Further, diode D₁₁ can beconfigured to keep the input voltage from grounding.

Referring now to FIG. 6A, shown is a schematic diagram of a fourthexample AC/DC power converter in accordance with embodiments of thepresent invention. AC/DC power converter 600 can include inductor L₆ asthe first energy storage component, transformer T₃ can include primarywinding W_(p3) and secondary winding W_(s3) as the second energy storagecomponent, and capacitor C₁₀ as the third storage component.

Referring now to FIG. 6B, shown as an example conduction path of theAC/DC power converter of FIG. 6A in a first operation mode. In the firstoperation mode, power switch Q₄ is turned on, and the inductor currentof inductor L₆ can continue to increase to store energy in inductor L₆through a first path (denoted by an encircled 1), which can includediode D₁₂, inductor L₆, power switch Q₄, and capacitor C₁.Simultaneously, the inductor current of inductor W_(p3) can continue toincrease to store energy in primary winding W_(p3) through a second path(denoted by an encircled 2), which can include primary winding W_(p3),power switch Q₄, diode D₂₇, and capacitor Q₁₀.

Referring now to FIG. 6C, shown is an example conduction path of theAC/DC power converter of FIG. 6A in a second operation mode. In thesecond operation mode, inductor current of inductor L₆ can continue todecrease to release energy to capacitor C₁₀ through charging in a thirdpath (denoted by an encircled 3), which can include inductor L₆, diodeD₁₃ and capacitor C₁₀. When the capacitance of capacitor C₁₀ issufficiently large, voltage V_(bus) across capacitor C₁₀ can bemaintained as substantially constant with minimal fluctuation.Simultaneously, the inductor current of secondary winding W_(s3) cancontinue to decrease to release energy to the load through a fourth path(denoted by an encircled 4), which can include inductor W_(s3), diodeD₁₄, and capacitor C₁₁.

Here, the first and third paths can form a boost-buck power stage toreceive half-sinusoid DC input voltage and generate constant voltageV_(bus) across capacitor C₁₀ with a sufficiently large capacitance.Also, the second and fourth paths can form a flyback power stage toreceive voltage V_(bus) across capacitor C₁₀, and to generate asubstantially constant output voltage V_(o) and a substantially constantoutput current I_(o) to drive the load (e.g., LED lamps) through thefourth path. Also, the first and second paths of the AC/DC powerconverter of FIG. 6A can share power switch Q₄ and controlling anddriving circuit 603. Further, diode D₂₇ can be configured to keep theinductor current of inductor L₆ from flowing to primary winding W_(p3)in the second operation mode.

With reference to FIG. 7A, shown is a schematic diagram of a fifthexample AC/DC power converter in accordance with embodiments of thepresent invention. IAC/DC power converter 700 can include inductor L₇ asthe first energy storage component, transformer T₄ can include primarywinding W_(p4) and secondary winding W_(s4) as the second energy storagecomponent, and capacitor C₁₂ as the third storage component.

The conduction paths of AC/DC power converter 700 in various operationmodes will be described in conjunction with the following figures fromFIG. 7B to FIG. 7E. Some components are shared to form the two powerstages of AC/DC power converter 700, such as power switch Q₅ andcontrolling and driving circuit 703. One power stage may be configuredto achieve the power factor correction to make the peak current envelope(current through inductor L₇) as a sinusoid waveform, while the otherpower stage may be configured to achieve a substantially constant outputcurrent to supply to the load (e.g., LED lamps). The voltage acrosscapacitor C₁₂ can be configured to provide supply to the other powerstage. Also, operation of diodes D₁₆ and D₁₇ may be determined based ona comparison between the current through inductor L₇ and the currentthrough primary winding W_(p4).

Referring now to FIG. 7B, shown are example waveforms of the current(i_(L7)) through inductor L₇ and the current (i_(Wp4)) through primarywinding W_(p4). In view that the on time of power switch Q₅ iscontrolled to be substantially constant in each switch cycle, the peakvalue of current (i_(L7)) may be in direct proportion to half-sinusoidDC input voltage V_(in), and the current (i_(Wp4)) can be presented as atriangle waveform with a constant peak value. During the interval fromtime t₁ to time t₂, current (i_(L7)) is higher than current (i_(Wp4)),and diode D₁₇ is on. During the interval from time t₀ to time t₁ and theinterval from time t₂ to time t₃, current (i_(L7)) is lower than current(i_(Wp4)), and diode D₁₆ is on.

Referring now to FIG. 7C, shown are example conduction paths when bothpower switch Q₅ and diode D₁₇ are turned on. Capacitor C₁₂ can becharged through power switch Q₅, diode D₁₇, and the current of inductorL₇ can continue to increase in a first path (denoted by an encircled 1).Also, the current of primary winding W_(p4) can continue to increase tostore energy through a second path (denoted by an encircled 2), whichcan include diode D₁₇ and capacitor C₁₂. Here, resistor R_(sen) can alsobe included in the second path to sense the current flowing throughprimary winding W_(p4) accurately since the current of the second pathis independent of the current of the first path. The common node of bothresistor R_(sen) and primary winding W_(p4) can be coupled to an equalpotential of the system, so the voltage of the other terminal ofresistor R_(sen) can be representative of the current flowing throughprimary winding W_(p4).

With reference to FIG. 7D, shown are example conduction paths when powerswitch Q₅ is turned on and diode D₁₆ is on. The current of inductor L₇can continue to increase through the first path, which can include diodeD₁₅, power switch Q₅, resistor R_(sen), primary winding W_(p4), andinductor L₇. The current of primary winding W_(p4) can include both thecurrent of the first path and the current of the second path, which caninclude diode D₁₆, power switch Q₅, resistor R_(sen), primary windingW_(p4), and capacitor C₁₂. Also, capacitor C₁₂ can discharge through thesecond path.

Referring now to FIG. 7E, shown is an example conduction path of theAC/DC power converter of FIG. 7A when power switch Q₅ is turned off. Inthis operation mode, the inductor current of inductor L₇ can continue todecrease to release energy to capacitor C₁₂ through charging in a thirdpath (denoted by an encircled 3), which can include inductor L₇, diodeD₁₈, and capacitor C₁₂. When the capacitance of capacitor C₁₂ issufficiently large, voltage V_(bus) across capacitor C₁₂ can bemaintained as substantially constant with minimal fluctuation.Simultaneously, the inductor current of secondary winding W_(s4) cancontinue to decrease to release energy to the load through a fourth path(denoted by an encircled 4), which can include inductor W_(s4), diodeD₁₉, and capacitor C₁₃.

Here, the first and third paths can form a buck power stage to receivehalf-sinusoid DC input voltage V_(in) and generate constant voltageV_(bus) across capacitor C₁₂ with a sufficiently large capacitance. Acapacitor with lower capacitance and cost can be configured as capacitorC₁₂ due to the lower voltage V_(bus) across capacitor C₁₂ generated bythe buck power stage. The second and fourth paths can form a flybackpower stage to receive voltage V_(bus) across capacitor C₁₂, and togenerate a substantially constant output voltage V_(o) and asubstantially constant output current I_(o) to drive the load (e.g., LEDlamps) through the fourth path. The first and second paths of the AC/DCpower converter of FIG. 7A can share power switch Q₅ and controlling anddriving circuit 703. Here, diode D₁₅ can be configured to keep thecurrent from reflowing to the input terminal when the DC input voltageV_(in) is lower.

Referring now to FIG. 8A, shown is a schematic diagram of a sixthexample AC/DC power converter in accordance with embodiments of thepresent invention. AC/DC power converter 800 can include inductor L₈ asthe first energy storage component, inductors L₉₁ and L₉₂ as the secondenergy storage component, and capacitor C₁₅ as the third energy storagecomponent. Also, a first path (denoted by an encircled 1), a second path(denoted by an encircled 2), a third path (denoted by an encircled 3),and a fourth path (denoted by an encircled 4), will be discussed withreference to FIGS. 8B and 8C.

Here, the first and third paths can form a boost power stage to receivehalf-sinusoid DC input voltage V_(in), and to generate a constantvoltage V_(bus) across capacitor C₁₅. The second and fourth paths canform a buck power stage to receive voltage V_(bus), and to generate asubstantially constant output current I_(o) to drive the load (e.g., LEDlamps). Also, the boost power stage and the buck power stage can sharepower switch Q₆ and controlling and driving circuit 803.

Referring now to FIG. 8B, shown as an example conductive path in a firstoperation mode of the AC/DC power converter of FIG. 8A. In the firstoperation mode, power switch Q₆ is turned on. Inductor current i_(L8) ofinductor L₈ can continue to increase to store energy in the first path,which can include inductor L₈, diode D₂₁, and power switch Q₆.Simultaneously, inductor current flowing through coupled inductors L₉₁and L₉₂ can continue to increase in the second path, which can includecapacitor C₁₅, capacitor C₁₄, coupled inductors L₉₁ and L₉₂, and powerswitch Q₆. Also, resistor R_(sen) can be arranged between a common nodeof power switch Q₆ and an output terminal of the rectifier bridge BR,and an equivalent potential can also be included in the second path toaccurately sense the inductor current flowing through coupled inductorsL₉₁ and L₉₂.

Referring now to FIG. 8C, shown is an example conductive path in asecond operation mode of the AC/DC power converter of FIG. 8A. In thesecond operation mode, power switch Q₆ is turned off. In the third path,which can include inductor L₈, diode D₂₀, and capacitor C₁₅, theinductor current through inductor L₈ can continue to decrease to releaseenergy to capacitor C₁₅ by charging. When the capacitance of capacitorC₁₅ is sufficiently large, voltage V_(bus) across capacitor C₁₅ can bemaintained as substantially constant with minimal fluctuation.Simultaneously, the inductor current of coupled inductors L₉₁ and L₉₂can continue to decrease to release the energy to the load through thefourth path, which can include inductor L₉₂, diode D₂₂, and capacitorC₁₄.

The drop rate of the inductor current can be increased significantly dueto the configuration of coupled inductor L₉₁ and L₉₂ to decrease theduration of the switching cycle. The circuit structure and theconductive paths of different operation modes of the AC/DC powerconverter of FIG. 8A have been described. The controlling principles ofpower factor correction and constant output electric signal of the AC/DCpower converter of FIG. 8A will be described below.

Referring now to FIG. 9A, shown is a schematic diagram of a seventhexample AC/DC power converter in accordance with embodiments of thepresent invention. AC/DC power converter 900 can include a coupledinductor including inductors L₁₀₁ and L₁₀₂ as the first energy storagecomponent. Transformer T₅ can include primary winding W_(p5) andsecondary winding W_(s5) as the second energy storage component, andcapacitor C₁₇ can be configured as the third energy storage component.Also, a first path (denoted by an encircled 1), a second path (denotedby an encircled 2), a third path (denoted by an encircled 3), and afourth path (denoted by an encircled 4), will be discussed withreference to FIG. 9C.

Here, the first and third paths can form a boost power stage to receivehalf-sinusoid DC input voltage V_(in), and to generate a constantvoltage V_(bus) across capacitor C₁₅. The second and fourth paths canform a flyback power stage to receive voltage V_(bus), and to generateconstant output current I_(o) to drive the load (e.g., LED lamps). Also,the boost power stage and the flyback power stage can share power switchQ₇ and controlling and driving circuit 903.

Referring now to FIG. 9B, shown is an example conductive path in a firstoperation mode of the AC/DC power converter of FIG. 9A. In the firstoperation mode, power switch Q₇ is turned on. Current through coupledinductors L₁₀₁ and L₁₀₂ can continue to increase to store energy in thefirst path, which can include coupled inductors L₁₀₁ and L₁₀₂, diodeD₂₃, and power switch Q₇. Simultaneously, current through primarywinding W_(p5) can continue to increase in the second path, which caninclude capacitor C₁₇, diode D₂₅, primary winding W_(p5), and powerswitch Q₇. Also, resistor R_(sen) can be arranged between a common nodeof power switch Q₆ and in output terminal of rectifier bridge BR, and anequivalent potential can be included in the second path to accuratelysense current through primary winding W_(p5).

Referring now to FIG. 9C, shown is an example conductive path in asecond operation mode of the AC/DC power converter of FIG. 9A. In thesecond operation mode, power switch Q₇ is turned off. In the third path,which can include inductor L₁₀₁, diode D₂₄, and capacitor C₁₇, theinductor current of inductor L₁₀₁ can continue to decrease to releaseenergy to capacitor C₁₇ by charging. When the capacitance of capacitorC₁₇ is sufficiently large, voltage V_(bus) across capacitor C₁₇ can bemaintained as substantially constant with minimal fluctuation.Simultaneously, the inductor current of secondary winding W_(s5) cancontinue to decrease to release the energy to the load through thefourth path, which can include secondary winding W_(s5), diode D₂₆, andcapacitor C₁₆.

The foregoing descriptions of specific embodiments of the presentinvention have been presented through images and text for purpose ofillustration and description of the AC/DC power converter circuit andmethods. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching, such as different converter topologies, and alternatives ofthe type of the power switch for different applications.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

1. An AC/DC power converter, comprising: a) a rectifier bridge and afilter capacitor configured to convert an external AC voltage to ahalf-sinusoid DC input voltage; g) a first power stage having a firstconverter topology and being configured to receive said half-sinusoid DCinput voltage, said first power stage comprising a first magneticcomponent, a capacitive component, a controlling and driving circuit,and a power transistor, wherein said first power stage is configured toprovide power factor correction (PFC) of a first current flowing throughsaid first magnetic component relative to said half-sinusoid DC inputvoltage; h) a second power stage having a second converter topology andcomprising a second magnetic component, said capacitive component, andsaid power transistor, wherein said capacitive component is common tosaid first and second power stages, and wherein said second power stageis configured to provide constant current regulation of an outputcurrent of said AC/DC power converter; and i) a sampling resistorcoupled between said power transistor and ground.
 2. The AC/DC powerconverter of claim 1, wherein said sampling resistor is configured todetect a second current in said second power stage, and to generate afeedback signal in said a first operation mode.
 3. The AC/DC powerconverter of claim 2, wherein said controlling and driving circuit isconfigured to generate a driving signal to drive said power switchtransistor based on said feedback signal.
 4. The AC/DC power converterof claim 1, wherein: a) said first magnetic component comprises a firstinductor; and b) said second magnetic component comprises a secondinductor.
 5. The AC/DC power converter of claim 2, wherein: a) saidpower switch transistor is on when in said first operation mode; and b)said power switch transistor is off when in a second operation mode. 6.The AC/DC power converter of claim 1, wherein said second magneticcomponent comprises a transformer.
 7. The AC/DC power converter of claim1, wherein a voltage across said sampling resistor is configured torepresent a peak inductor current.
 8. The AC/DC power converter of claim1, wherein each of said first and second power stages comprises atopology selected from: buck, boost, flyback, and boost-buck.
 9. TheAC/DC power converter of claim 1, wherein said output current isconfigured to drive a light-emitting diode (LED) load.
 10. The AC/DCpower converter of claim 9, wherein said LED load is coupled to saidsecond magnetic component and said capacitive component.
 11. The AC/DCpower converter of claim 1, further comprising: a) a first diode havingan anode coupled to said first magnetic component and a cathode coupledto a common node; and b) a second diode having an anode coupled to saidsecond magnetic component and a cathode coupled to said common node. 12.The AC/DC power converter of claim 11, wherein said power transistor iscoupled to said common node.
 13. The AC/DC power converter of claim 11,further comprising a third diode having an anode coupled to said commonnode and a cathode coupled to said capacitive component.
 14. The AC/DCpower converter of claim 1, wherein said second magnetic component isconfigured to operate in a boundary conduction mode (BCM).
 15. The AC/DCpower converter of claim 1, wherein said first converter topologycomprises a boost topology, and said second converter topology comprisesa flyback topology.
 16. The AC/DC power converter of claim 1, whereinsaid first converter topology comprises a buck-boost topology, and saidsecond converter topology comprises a flyback topology.
 17. The AC/DCpower converter of claim 1, wherein said first converter topologycomprises a boost topology, and said second converter topology comprisesa buck topology.
 18. The AC/DC power converter of claim 1, wherein saidfirst converter topology comprises a flyback topology, and said secondconverter topology comprises a buck topology.
 19. The AC/DC powerconverter of claim 1, further comprising: a) a first diode having ananode coupled to said first magnetic component and a cathode coupled toa common node; and b) a second diode having an anode coupled to saidfirst magnetic component and a cathode coupled to said second magneticcomponent.
 20. The AC/DC power converter of claim 19, wherein saidcapacitive component is coupled to said second magnetic component andground.